Chilian System. 1^ 



Cordillera of Chili, simultaneously with the earthquakes which 

 ravage the coast, near to which they take place with their 

 maximum of intensity. 



Another peculiarity which distinguishes the Chilian system 

 from the Bolivian system, is the presence of patches, which 

 are still problematical, of the Jurassic formation, and of largely 

 developed masses of the cretaceous formation, in beds much 

 dislocated and raised to great heights. According to M. D'Or- 

 bigny, it was after the cretaceous period, but before the period 

 of the tertiary deposits, that the Chilian system had its origin. 

 It was produced by the eruption of the porphyritic rocks, or 

 perhaps only of a portion of these rocks, which, in South 

 America, are of various kinds. M. D'Orbigny found at Co- 

 bija on the coast of the Pacific, sienitic porphyries of a blackish 

 colour and very compact ; at the Morro of Arica, pyroxenic 

 porphyries ; at Palca (Bolivia), and at Machacamarca, sienitic 

 porphyries ; in the mountains of Cobija and of Palca (Peru), 

 and throughout the whole western line of the Cordilleras, he 

 found a great variety of old amygdaloidal wackes, containing 

 a large quantity of different substances ; at the Missions, there 

 is a greyish or violet-coloured amygdaloidal rock. Porphyritic 

 rocks have also been observed by Messrs Gay, Darwin, and 

 Domeyko, in different parts of the Cordillera of Chili. 



According to M. D'Orbigny, the termination of the creta- 

 ceous period was marked in South America by a series of dis- 

 locations, which occurred to the west of the land already pro- 

 jecting from the sea, and which gave to the Cordillera of Chili 

 its first relief, by permitting the elevation of a continuous 

 series of porphyritic masses. This vast porphyritic eruption 

 took place in the direction from N. 5° E. to 5° W. between 

 the Straits of Magellan and the junction of the Chilian sys- 

 tem with the Bolivian system, which the band of eruptive rock 

 has accompanied to the west, elevating the cretaceous forma- 

 tion of the plateau of Guancavelica. The violent commotion 

 of the water caused by this movement had, as its result, ac- 

 cording to M. D'Orbigny, the formation of the Guaranian ter- 

 tiary deposit, which covers the province of Moxos, and which 

 seems to be spread over the bottom of a large portion of the 



